The proposed study addresses the possible impact of environmental lead on the developing immune system of young children. Data from animal model systems indicate that lead is an immunosuppressive agent at levels far below those required for overt toxicity. But there are difficulties in extrapolating these data to human systems. A number of urban children between the ages of 1.5 to 6 years with blood lead levels >25 mug/100 ml has been identified in the Springfield, Greene County area of Missouri through participation in local WIC (Women, Infants, and Children) and Lead Poisoning Prevention Programs. Participants in these programs are presently required to have periodic blood tests, as well as special counseling in continuing attempts to identify nutritional deficiencies as well as possible sources of lead and to encourage efforts to reduce body burden. This group of children, together with appropriately matched controls identified during the same screening procedures, offer an ideal opportunity to investigate possible correlations between blood lead concentrations and various immunological parameters. Planned assays to assess function of B-lymphocytes are serum Ig concentrations; specific antibody titer vs. tetanus toxoid, measles, or polio; and B cell count. Proposed assays to determine T lymphocyte function are T cell count; ratio of T-helper/T-suppressor subclasses; and response to mitogens. Phagocytic function will be measured by monocyte phagocytosis of yeast cells. The specific aims of this study are as follow: 1. Determine appropriate sample size and set up control and experimental groups after statistical analysis of data from normal controls for each proposed assay. 2. Perform screening assays on an initial sample and 12-month follow- up sample to determine which component(s) of the immune system are sensitive to lead exposure. 3. Evaluate data from the screening assays to determine those most clearly indicating detrimental effects of lead for use in an expanded study and to assess the need for a longitudinal study. The data generated by this proposal will provide invaluable information on the possible detrimental health effects of in vivo lead exposure in a population at great risk for such exposure. It will allow selection of the most sensitive aspect of the immune response for further and more definitive testing. In addition, evaluation of the follow-up samples will assess the feasibility and need for a longitudinal study on effects of chronic lead exposure on the developing immune system.